The purposes of this study is to see if measuring the amount of Cytomegalovirus (CMV) in the blood using three new blood tests can predict the development of disease caused by CMV in persons with AIDS. The tests being studied can detect the presence of CMV and also count how much CMV is in the blood. This study will try to determine if people with CMV in their blood are at greater risk for developing CMV disease and to see if a higher amount of CMV found means a greater chance of developing CMV disease. The study will also look at the level of HIV in the blood to see if the amount of HIV a person has in their blood is a factor in developing CMV disease.